U.S. Pat. No. 7,837,238 to Krausz describes a pipe coupling that combines an elastomeric seal member with a grip ring. The grip ring is formed of wedge-shaped grip elements that are radially spaced from one another. The grip elements are formed with teeth that face inwards towards the center of the ring. A single fastener (e.g., bolt and nut or other tightenable screw) is provided, which when tightened in a direction transverse to the axial length of the pipe, presses both the elastomeric seal member and the grip ring against the surface of the pipe.
FIGS. 1A and 1B illustrate the prior art grip element 1 of U.S. Pat. No. 7,837,238. Grip element 1 is made of sheet metal, such as a medium-hardness steel alloy, by stamping or punching or other sheet metal forming processes. The terms “stamping” and “punching” are used as interchangeable terms in this application. Grip element 1 has a wedge shape including a sloped surface 2 on which teeth 3 and 4 are formed. Grip element 1 is provided with an array of large 3 and small 4 gripping teeth. The sharp edges of all teeth face outwards. The large teeth 3 project from the surface 2 further than the small teeth 4.
Small teeth 4 are shaped as a cluster of pointed barbs, which may be punched out the sheet metal. Large teeth are shaped as oval grater barbs, which may be punched out the sheet metal.
Grip element 1 can be used with both metal and plastic pipes without requiring any adjustment. The larger teeth penetrate the surface of a plastic pipe to a depth sufficient to prevent axial withdrawal. The smaller and thus stronger teeth penetrate the surface of a metal pipe even if the larger teeth collapse.
As is seen in the underside view in FIG. 1B, because grip element 1 is stamped, teeth 3 and 4 are formed all the way through the thickness of sloped surface 2. The “negative” undersides of the teeth 3 and 4 are seen on the back of surface 2.